com.expleague.ml.loss.LLX2 Maven / Gradle / Ivy
package com.expleague.ml.loss;
import com.expleague.commons.math.FuncC1;
import com.expleague.commons.math.vectors.Vec;
import com.expleague.commons.math.vectors.impl.vectors.ArrayVec;
import com.expleague.ml.data.set.DataSet;
import com.expleague.ml.TargetFunc;
import static java.lang.Math.exp;
import static java.lang.Math.log;
/**
* We use value representation = e^{-(x + 1)^2}.
* User: solar
* Date: 21.12.2010
* Time: 22:37:55
*/
public class LLX2 extends FuncC1.Stub implements TargetFunc {
private final Vec target;
private final DataSet> owner;
public LLX2(final Vec target, final DataSet> owner) {
this.target = target;
this.owner = owner;
}
@Override
public Vec gradient(final Vec point) {
final Vec result = new ArrayVec(point.dim());
for (int i = 0; i < point.dim(); i++) {
final double x = point.get(i) + 1;
if (target.get(i) > 0) // positive example
result.set(i, -2 * x);
else // negative
result.set(i, 2 * x/(exp(x*x) - 1));
}
return result;
}
@Override
public int dim() {
return target.dim();
}
@Override
public double value(final Vec point) {
double result = 0;
for (int i = 0; i < point.dim(); i++) {
final double x = point.get(i) + 1;
final double pX = exp(-x * x);
if (target.get(i) > 0) // positive example
result -= log(pX);
else // negative
result -= log(1 - pX);
}
return result;
}
@Override
public DataSet> owner() {
return owner;
}
}
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